This invention relates to a kit for improving the service life of a dynamo electric machine, and to a dynamo electric machine modified by the use of such a kit.
The term xe2x80x9cservice lifexe2x80x9d is used herein to indicate a recommended operational period between maintenance times at which the machine is withdrawn from service for scheduled maintenance.
The invention is particularly, but not exclusively, concerned with dynamo electric machines for use in conjunction with aircraft gas turbine engines, particularly starter-motor/generator units. The present inventor has recognised that recent improvements in the design and manufacture of such dynamo electric machines has produced a situation in which the service life is governed by the wear rate of the brushes of the machine and has recognised that if the useful life of the brushes of the machine can be extended then the service life can be extended by a corresponding amount up to the point at which the service life of some other component of the machine is reached.
In accordance with the present invention there is provided a kit for use with a dynamo electric machine of the kind having a yoke, apertures in the yoke through which brushes of the machine are accessible, and a brush holder assembly for supporting the brushes in a predetermined alignment in relation to a commutator or slip-rings of the machine, the kit comprising replacement brushes of a length exceeding the length of the conventional brushes for the machine, and a cover component comprising a cylindrical band for attachment around the exterior of the yoke to close said brush access apertures in use, said band including radially outwardly extending protrusions to be positioned over said apertures of the yoke in use and thereby to accommodate the additional length of the replacement brushes.
Preferably the kit further includes replacement springs for attachment to respective brush holders and engagable with the outer ends of the replacement brushes to urge the brushes radially inwardly of the machine in use throughout the increased wear length of the replacement brushes.
Conveniently said replacement springs comprise constant force springs together with clip means for anchoring the constant force springs to their respective brush holder.
Desirably the kit further includes replacement brush holders shaped to receive said replacement springs and said replacement brushes.
In another aspect the invention resides in a brush replacement kit for use with a dynamo electric machine of the kind having a yoke, apertures in the yoke through which brushes of the machine are accessible, and a brush holder assembly for supporting the brushes in a predetermined alignment in relation to a commutator or slip-ring assembly of the machine, the kit comprising replacement brushes of a length exceeding the length of the conventional brushes for the machine, replacement springs for attachment to respective brush holders and engagable in use with outer ends of respective replacement brushes to urge the brushes radially inwardly of the machine in use throughout the increased wear length of the replacement brushes, said replacement springs comprising constant force springs together with clip means for anchoring the constant force springs to a respective brush holder, replacement brush holders shaped to receive said replacement springs and said replacement brushes, and a cover component comprising a cylindrical band for attachment around the exterior of the yoke to close said brush access apertures in use, said band including radially outwardly extending protrusions to be positioned over said apertures of the yoke in use and thereby to accommodate the additional length of the replacement brushes.
The invention also resides in a dynamo electric machine fitted with a kit of the kind defined above.
In a further aspect of the invention there is provided a dynamo electric machine of the kind having a yoke, apertures in the yoke through which brushes of the machine are accessible, a brush holder assembly for supporting the brushes in a predetermined alignment in relation to a commutator or slip-ring assembly of the machine, brushes of a length exceeding the length of the conventional brushes for the machine, spring arrangements attached to respective brush holders and engaging with outer ends of respective brushes to urge the brushes radially inwardly of the machine in use throughout the increased wear length of the brushes, and a cover component comprising a cylindrical band for attachment around the exterior of the yoke to close said brush access apertures in use, said band including radially outwardly extending protrusions to be positioned over said apertures of the yoke in use and thereby to accommodate the additional length of the brushes.
Preferably said spring arrangements comprise constant force springs together with clip means for anchoring the constant force springs to a respective brush holder, and said brush holders being shaped to receive said constant force springs together with clip means, and said brushes.